Bearing is one of the most important fundamental part of the kinematic mechanism. Bearing is used for transmitting power, supporting the rotational parts and ensuring the rotating precision. Bearing is widely used in the industries and our daily lives, such as power generating equipment, aircraft, rocket, ship, automobile, train, electrical appliance, etc. Bearing is the key part to maintain normal running of the machine. Generally, a set of bearing is composed of inner ring, outer ring, ball and cage. There is raceway on the inner surface of the outer ring and the outer surface of the inner ring. One function of the raceway is providing the movement track of the ball, and the other function is constraining the movement direction of the ball.
Bearing works in the high speed, high temperature, fluctuating load, friction and vibration environment. Therefore, it is feasible to breakdown because of fatigue failure. Although the shape of bearing is quite simple, its manufacturing precision is very high and extremely long fatigue life is required. Hence, it is one of the most difficult part to be manufactured.
Manufacturing procedure of bearing is multi-steps. Generally, forging is the first step to provide original workpiece for the further processing. If the quality of original workpiece is not well, e.g., machining allowance is too large, grain size is big, forging flowlines are interrupted, not only the processing time becomes long, but also the fatigue life of the bearing will be greatly shortened. Hence, it is very important to provide high-precision, high-quality, fatigue-resistant forging workpiece for further manufacturing long-life bearing.
Traditional fabricating flowchart of the bearing ring forging, especially for the high temperature alloys, is: “saw-cutting blanking→heating→upsetting→punching blind hole→punching through hole→first pass ring rolling→heating→second pass ring rolling→ . . . →machining the raceway”. The ellipsis represents the possible additional passes of heating and ring rolling process for high temperature alloys, annealing, shot blasting and acid cleaning procedures. The “saw-cutting blank→heating→upsetting→punching blind hole→punching through hole” procedure can be collectively called ring-billet making process. The traditional ring forging processing line is long. The dimensional precision of the obtained ring forging is very low and the machining allowance is quite large. Furthermore, the rolling temperature cannot be controlled exactly and the requirement of forming force is relatively large. Especially, for the metals or alloys with high hot strength or low ductility, the forging cannot be formed within one pass of rolling. Generally two or more passes rolling is needed for the metals or alloys with high hot strength or low ductility. More importantly, the raceway cannot be formed integrally in the rolling process, and it is machined after ring rolling, which will cut down the forging flowlines and greatly damage the fatigue life of the bearing. Therefore, a compact near-net forming method of fabricating the anti-fatigue bearing ring forging is anticipated.